Software Requirements Specifications (SRS)
A Software Requirements Specification (SRS) is a document that describes what a software system should do, including its functionality, performance requirements, and constraints. Formalised as IEEE 830-1998, the practice of writing detailed specifications before implementation was common in the waterfall era but fell out of favour as agile methodologies prioritised working software over comprehensive documentation. However, perhaps it's coming back in favour again in the LLM era via Spec-First LLM Development.